| Abstract: | Phase transition and band structure tuned by uniaxial and biaxial strains are systematically investigated based on the density-functional theory for ordered Al_(1/2)Ga_(1/2)N alloys of complex structures.Although the structural transformations to graphite-like from wurtzite are energetically favorable for both types of strain,the phase transitions are different in nature:the second-order transition induced by uniaxial strain is jointly driven by the mechanical and dynamical instabilities and the first-order transition by biaxial strain only by the mechanical instability.The wurtzite phase always shows the direct band gap,while the band gap of the graphite-like phase is always indirect.Furthermore,the band gaps of the wurtzite phase can be reduced by both types of strain,while that of the graphite-like phase is enhanced by uniaxial strain and is suppressed by biaxial strain. |
